Meltblown web

ABSTRACT

The present invention is directed to a multiple component meltblown web comprised of at least 95% by weight of meltblown fibers having an average effective diameter of less than 10 microns, said multiple component meltblown web comprised of a first polymer component and a second polymer component distinct from said first polymer component, said first polymer component being comprised of from 1% to 99% by weight of a first polymer and from 99% to 1% by weight of a second polymer.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] This invention relates to webs of meltblown fibers and tocomposite nonwoven fabrics that include a web of meltblown fibers. Morespecifically, the invention relates to meltblown webs that includemultiple component fibers wherein a component of the fibers is comprisedof a blend of polymers.

[0003] 2. Description of Related Art

[0004] Thermoplastic resins have been extruded to form fibers for manyyears. These resins include polyolefins, polyesters, polyamides, andpolyurethanes. The extruded fibers have been made into a variety ofnonwoven fabrics including composite laminates such asspunbond-meltblown-spunbond (“SMS”) composite sheets. In SMS composites,the exterior layers are spunbond fiber layers that contribute strengthto the overall composite, while the core layer is a meltblown fiberlayer that provides barrier properties.

[0005] U.S. Pat. No. 5,616,408 discloses an SMS composite fabric inwhich the meltblown fibers are comprised of a blend of polyethylene anda polyethylene processing stabilizing component. The stabilizingcomponent is added to the polyethylene so as to stiffen the soft, highlyelongatable polyethylene resin so that the resin can be meltblownwithout substantial formation of shot, polymer globules and the like.The stabilizing component is disclosed as being another polymer such asa polyolefin, polyester or polyamide added to the polyethylene in anamount of about 1 to 15 percent by weight based upon the weight to thepolyethylene polymer.

[0006] U.S. Pat. No. 4,547,420 discloses bicomponent meltblown fibersand webs made from such fibers. One of the components is crystallizablepoly(ethylene terephthalate) and the other component is polypropylene.

SUMMARY OF THE INVENTION

[0007] A first embodiment of the present invention is directed to amultiple component meltblown web comprised of at least 95% by weight ofmultiple component meltblown fibers having an average effective diameterof less than 10 microns, the multiple component meltblown fiberscomprised of a first polymer component and a second polymer componentdistinct from the first polymer component, the first polymer componentbeing comprised of from 1% to 99% by weight of a first polymer and from99% to 1% by weight of a second polymer wherein the first and secondpolymers are selected from the group consisting of polyolefins,polyesters, polyamides, polystyrene, polyurethanes, fluoropolymers,olefinic ionomer resins, random co-polymers of ethylene and methacrylicacid, and random co-polymers of ethylene and vinyl acetate.

[0008] In another embodiment, the present invention is directed to amultiple component meltblown web comprised of at least 95% by weight ofmeltblown fibers having an average effective diameter of less than 10microns, the meltblown fibers comprised of a first polymer component anda second polymer component distinct from the first polymer component,the first polymer component being comprised of from 1% to 99% by weightof a first polymer and from 99% to 1% by weight of a second polymerwherein the first and second polymers consist essentially ofnon-elastomeric polymers.

[0009] In another embodiment, the present invention is directed to amultiple component meltblown web comprised of at least 95% by weight ofmeltblown fibers having an average effective diameter of less than 10microns, the meltblown fibers comprised of a first polymer component anda second polymer component distinct from the first polymer component,the first polymer component being comprised of from 1% to 99% by weightof a first polymer and from 99% to 1% by weight of a second polymerwherein the first and second polymers consist essentially of elastomericpolymers.

[0010] In another embodiment, the present invention is directed to acomposite sheet comprising a first fibrous layer having a first side andan opposite second side, a second fibrous layer bonded to the first sideof the first fibrous layer, the first fibrous layer being a multiplecomponent meltblown web comprised of at least 95% by weight of multiplecomponent meltblown fibers having an average effective diameter of lessthan 10 microns, the multiple component meltblown fibers comprised of afirst polymer component and a second polymer component distinct from thefirst polymer component, the first polymer component being comprised offrom 1% to 99% by weight of a first polymer and from 99% to 1% by weightof a second polymer, the second fibrous layer comprised of at least 95%by weight of second layer fibers having an average effective diameterthat is greater than the average effective diameter of the meltblownfibers of the first fibrous layer.

BRIEF DESCRIPTION OF THE DRAWINGS

[0011] The accompanying drawings, which are incorporated in andconstitute a part of this specification, illustrate the presentlypreferred embodiments of the invention.

[0012]FIG. 1 is a schematic perspective view of a meltblown webaccording to the invention.

[0013]FIG. 2 is a diagrammatical cross-sectional view of a compositenonwoven fabric incorporating the meltblown web of FIG. 1.

[0014]FIG. 3 is a diagrammatical cross-sectional view of anothercomposite nonwoven fabric incorporating the meltblown web of FIG. 1.

[0015]FIG. 4 is a schematic diagram of a portion of an apparatus usedfor producing the meltblown webs of the invention.

[0016]FIG. 5 is a schematic illustration of an apparatus for producing aspunbond nonwoven layer for use in the composite nonwoven fabric of theinvention.

[0017]FIG. 6 is schematic illustration of an apparatus for producing thecomposite nonwoven fabric of the invention.

DETAILED DESCRIPTION OF THE INVENTION

[0018] The term “polymer” as used herein, generally includes but is notlimited to, homopolymers, co-polymers (such as for example, block,graft, random and alternating co-polymers), terpolymers, etc. and blendsand modifications thereof. Furthermore, unless otherwise specificallylimited, the term “polymer” shall include all possible geometricalconfigurations of the material. These configurations include, but arenot limited to isotactic, syndiotactic and random symmetries.

[0019] The term “polyolefin” as used herein, is intended to mean any ofa series of largely saturated open chain polymeric hydrocarbons composedonly of carbon and hydrogen. Typical polyolefins include, but are notlimited to, polyethylene, polypropylene, polymethylpentene and variouscombinations of the ethylene, propylene, and methylpentene monomers.

[0020] The term “polyethylene” as used herein is intended to encompassnot only homopolymers of ethylene, but also co-polymers wherein at least85% of the recurring units are ethylene units.

[0021] The term “polypropylene” as used herein is intended to embracenot only homopolymers of propylene but also co-polymers where at least85% of the recurring units are propylene units.

[0022] The term “polyester” as used herein is intended to embracepolymers wherein at least 85% of the recurring units are condensationproducts of carboxylic acids and dihydroxy alcohols with polymerlinkages created by formation of an ester unit. This includes, but isnot limited to, aromatic, aliphatic, saturated, and unsaturated acidsand di-alcohols. The term “polyester” as used herein also includesco-polymers (such as block, graft, random and alternating co-polymers),blends, and modifications thereof. A common example of a polyester ispoly(ethylene terephthalate) which is a condensation product of ethyleneglycol and terephthalic acid.

[0023] The term “polystyrene” as used herein is intended to embrace notonly homopolymers of styrene but also co-polymers where at least 85% ofthe recurring units are styrene units.

[0024] The term “meltblown fibers” as used herein, means fibers formedby extruding a molten thermoplastic polymer through a plurality of fine,usually circular, capillaries as molten threads or filaments into a highvelocity gas (e.g. air) stream. The high velocity gas stream attenuatesthe filaments of molten thermoplastic polymer material to reduce theirdiameter to between 0.5 and 10 microns. Meltblown fibers are generallydiscontinuous fibers but may also be continuous. Meltblown fiberscarried by the high velocity gas stream are normally deposited on acollecting surface to form a web of randomly dispersed fibers.

[0025] The term “meltspun fibers” as used herein means small diameterfibers which are formed by extruding molten thermoplastic polymermaterial as filaments from a plurality of fine, usually circular,capillaries of a spinnerette with the diameter of the extruded filamentsthen being rapidly reduced. Meltspun fibers are generally continuous andhave an average diameter of greater than about 5 microns.

[0026] The term “nonwoven fabric, sheet or web” as used herein means astructure of individual fibers or threads that are positioned in arandom manner to form a planar material without an identifiable pattern,as in a knitted fabric.

[0027] The terms “multiple component fiber” and “multiple componentfilament” as used herein refer to any fiber or filament that is composedof at least two distinct polymers which have been spun together to forma single fiber or filament. The term “fiber” as used herein refers toboth discontinuous and continuous fibers. The at least two distinctpolymer (or fiber) components useable herein may be chemically differentor they may be chemically the same polymer, but having differentphysical characteristics, such as intrinsic viscosity, melt viscosity,die swell, density, crystallinity, and melting point or softening point.For example, the two fiber components may be linear low densitypolyethylene and high density polyethylene or a high viscositypolypropylene and a low viscosity polypropylene. The at least twodistinct polymer (or fiber) components are preferably arranged indistinct substantially constantly positioned zones across thecross-section of the multiple component fibers and may extendsubstantially continuously along the length of the fibers. Preferablythe multiple component fibers are bicomponent fibers which are made fromtwo distinct polymer (or fiber) components. Multiple component fibersare distinguished from fibers which are extruded from a homogeneous meltblend of polymeric materials. Multiple component fibers useful inpracticing the current invention include sheath-core and side-by-sidefibers. Preferably the multiple component meltblown fibers which formthe webs of the current invention are bicomponent fibers in which thetwo distinct polymers are arranged in a side-by-side configuration.

[0028] The term “multiple component web” as used herein refers to anonwoven web comprising multiple component fibers or filaments. The term“bicomponent web” as used herein refers to a multiple component webcomprising bicomponent fibers. Multiple component webs may include bothsingle component and multiple component fibers or filaments. The term“multiple component meltblown web” as used herein means a web comprisingmultiple component meltblown fibers spun from fine capillaries as moltenfilaments containing multiple and distinct polymer components, whichmolten filaments are attenuated by a high velocity gas stream anddeposited on a collecting surface as a web of randomly dispersed fibers.

[0029] Reference will now be made in detail to the presently preferredembodiments of the invention, examples of which are illustrated below.

[0030] A preferred embodiment of the meltblown web of the invention isshown in FIG. 1. The fine fiber layer 14 comprises a multiple componentmeltblown web formed from at least two polymer components simultaneouslyspun from a series of spinning orifices. According to the invention, atleast one of the polymer components comprises a blend of two or morepolymers. The fibers in the multiple component meltblown web 14generally have an average effective diameter of between about 0.5microns and 10 microns, and more preferably between about 1 and 6microns, and most preferably between about 2 and 4 microns. As usedherein, the “effective diameter” of a fiber with an irregular crosssection is equal to the diameter of a hypothetical round fiber havingthe same cross sectional area. The fibers of the meltblown web 14 aresufficiently long to be entangle with other fibers in the web. Uponbeing laid down, the entangled fibers of the web 14 form cohesive webstructure.

[0031] The configuration of the fibers in the bicomponent web 14 ispreferably a side-by-side arrangement in which most of the fibers aremade of two side-by-side polymer components that extend forsubstantially the whole length of each fiber. Alternatively, thesebicomponent fibers may have a sheath/core arrangement wherein onepolymer is surrounded by another polymer, an “islands-in-the-sea”arrangement in which multiple strands of one polymer are imbedded inanother polymer, or any other multiple component fiber structure.

[0032] According to the invention, the fine fibers of the layer 14 areproduced according to a multiple component meltblowing process, forexample a process in which two or more extruders supply melted polymercomponents to a die tip where the polymer components are passed throughfine capillary openings and pneumatically drawn by a jet of attenuatinggas (e.g. air) around the fine capillary openings in the die. The fibersare deposited on a collecting surface such as a moving belt or screen, ascrim, or another fibrous layer. Fibers produced by melt blowing may bediscontinuous or continuous fibers having an effective diameter in therange of about 0.5 to about 10 microns.

[0033] The fibers of the multiple component meltblown web of the layer14 can be meltblown using a meltblowing apparatus having capillary dieopenings like that shown in FIG. 4. In the sectional view of ameltblowing spin block 20 shown in FIG. 4, two different polymericcomponents are melted in parallel extruders (not shown) and meteredseparately by gear pumps (not shown) to conduits 25 and 26 that aredivided by a plate 27. At least one of the polymer components comprisesa mixture or blend of different polymers. The polymer blend can beformed by feeding the different polymers, in pelletized form, to a screwextruder. The extruder melts and mixes the polymer blend before feedingthe polymer blend to the spin block 20. In the spin block 20 the polymerblend component comes into contact with the other polymer component orcomponents as it moves toward a line of capillary orifices 21. Thesecond polymer component may be a single polymer or a blend of polymers.

[0034] Alternatively, the fibers of the multiple component meltblown webof the layer 14 can be meltblown using a meltblowing apparatus like thatdescribed in U.S. Pat. No. 4,795,668, which is hereby incorporated byreference. In such an apparatus, the different polymeric components aremelted in parallel extruders and metered separately through gear pumpsinto a die cavity. From the die cavity, the polymer components areextruded together through a line of capillary orifices. According toanother alternative, the polymer components can be fed, in an alreadylayered form, into the cavity of the spin block from which the capillaryorifices are supplied with the multiple component polymer stream. Apost-coalescent die, as disclosed in copending provisional applicationNo. 60/223,040, filed Aug. 4, 2000, in which the distinct polymercomponents are extruded through separate extrusion orifices and arecontacted and fused after exiting the capillaries to form multiplecomponent meltblown fibers, may also be used.

[0035] After exiting the capillary orifices, a jet of gas, e.g. hot air,supplied from the channels 28 attenuates the emerging polymer filamentsto form meltblown fibers. Without wishing to be bound by theory, it isbelieved that the air jet may fracture some of the meltblown fibers intoeven finer fibers. The resulting meltblown fibers are believed toinclude bicomponent fibers in which each fiber is made of two separatepolymer components that both extend the length of the meltblown fiber ina side-by-side configuration. It is also believed that some of thefractured fibers may contain just one polymer component. The fine fibersof layer 14 could alternatively be produced by other known meltblowingprocesses, as for example by the process wherein an individual airnozzle surrounds each capillary, as disclosed in U.S. Pat. No.4,380,570.

[0036] By making one or more of the components of the multiple componentmeltblown fibers from a blend of polymers, applicants have found thatthe spinning performance and meltblown web quality may be improved.Applicants have further found that it is possible to very specificallytailor the properties of the meltblown webs made from such bicomponentfibers. For example, by using a polymer blend in one component of ameltblown bicomponent web, it is possible to form a web of fibers thathave dissimilar polymer components but are also resistant to splitting.For example, bicomponent meltblown fibers can be meltblown where onecomponent is a polyester such as poly(ethylene terephthalate) and theother component is primarily a polyolefin such as polyethylene. Byblending a minor amount of a polyester polymer, such as poly(butyleneterephthalate) into the polyethylene, the polyethylene component shouldadhere more readily to the poly(ethylene terephthalate) component.Alternatively, a polymer, such as a fluoropolymer, can be blended intoone of the components in order to enhance splitting of the fibers.According to one preferred embodiment of the invention, the polymerblend component may further include a compatibilizer for the polymers inthe blend.

[0037] Polymers suitable for use in preparing the multiple componentmeltblown webs of the current invention include polyolefins, polyesters,polyamides, polystyrene, polyurethanes including those made by combininghard segments comprising 4,4-diphenyl-methane diisocyanate with softsegments comprising either a polyester or poly-ether based polyol suchas Pellethane® polyurethanes available from Dow Plastics,fluoropolymers, random co-polymers of ethylene and methacrylic acid suchas Nucrel® resins marketed by DuPont, olefinic ionomer resins such asrandom co-polymers of ethylene and methacrylic acid which have beenneutralized with metal ions such as sodium or magnesium for exampleSurlyn® ionomer resins marketed by DuPont, and random co-polymers ofethylene and vinyl acetate. Preferred polymers include polyethylene,polypropylene, poly(ethylene terephthalate), poly(trimethyleneterephthalate), poly(butylene terephthalate), poly(hexamethyleneadipamide), and poly(ε-caprolactam).

[0038] Preferred combinations of polymer components includepolyester/blend of a polyester and a polyolefin, polyolefin/blend of twodistinct polyolefins, and polyester/blend of a polyolefin with anolefinic ionomer resin. In a preferred embodiment wherein the multiplecomponent meltblown fibers are bicomponent fibers, preferredcombinations of polymer components include poly(ethyleneterephthalate)/blend of polyethylene with poly(butylene terephthalate),polypropylene/blend of a polyethylene with a polypropylene, andpoly(ethylene terephthalate)/blend of polyethylene with an ionomericrandom co-polymer of ethylene and methacrylic acid. The polymercomponents of the multiple component meltblown fibers may consistessentially of 100% elastomeric polymers or they may consist essentiallyof 100% non-elastomeric polymers. By “elastomeric polymer” is meant apolymer which in monocomponent meltspun fiber form, free of diluents,has a break elongation in excess of 100% and which when stretched totwice its length, held for one minute, and then released, retracts toless than 1.5 times its original length within one minute of beingreleased. As used herein, “non-elastomeric polymer” means any polymerwhich is not an elastomeric polymer.

[0039] The composite sheet 10 shown in FIG. 2 is a three layer compositefabric in which the inner layer is comprised of the multiple componentmeltblown web 14 described above. The fine fibers meltblown web 14 issandwiched between outer layers 12 and 16, which are each comprised oflarger and stronger and bonded fibers. The very fine fibers of innerlayer 14, when formed into the layer 14, can provide a barrier layerwith extremely fine passages. The bonded fiber layers 12 and 16 arecomprised of coarser and stronger fibers that contribute strength, andin some instances barrier, to the composite sheet. The composite sheetof the invention may alternatively be formed as a two layer composite18, as shown in FIG. 3. In the two layer composite sheet, the fine fiberlayer 14 is attached on just one side to the coarser and stronger bondedlayer 12. According to other alternative embodiments of the invention,the composite sheet may be made with multiple layers of fine fibers likethe layer 14, or it may be made with more than two layers of coarser andstronger fiber layers like the layers 12 and 16.

[0040] According to the invention, the larger and stronger bonded fibersof the layers 12 and 16 are conventional meltspun fibers or some othertype of strong spunbond fiber. Preferably, the meltspun fibers aresubstantially continuous fibers. Alternatively, the layers 12 and 16could be an air-laid or wet-laid staple fiber web or a carded webwherein the fibers are bonded to each other to form a strong webstructure. The fibers of layers 12 and 16 should be made of a polymer towhich the fine fibers of the core layer 14 can readily bond.

[0041] Layers 12 and 16 are preferably made from bicomponent meltspunfibers. The components of the meltspun fibers of the layers 12 and 16may consist of a single polymer or a blend of polymers. According to onepreferred embodiment of the invention, the meltspun fibers of layers 12and 16 comprise polyester/polyethylene bicomponent fibers. The polyestercomponent contributes to the strength to the fabric while thepolyethylene component makes the fabric softer and more drapable. Inaddition, the polyethylene component has a lower melting temperaturethan the polyester component of the fiber so as to make the fiber layers12 and 16 more readily bondable to the fine fibers of the core layer 14using a thermal bonding process. Alternatively, layers 12 and 16 couldbe comprised of a blend of single polymer component fibers, as forexample, a spunbond web wherein a portion of the fibers are polyethylenefibers and a portion of the fibers are polyester fibers.

[0042] According to the preferred embodiment of the invention, thelarger and stronger fibers of the layers 12 and 16 are substantiallycontinuous spunbonded fibers produced using a high speed melt spinningprocess, such as the high speed spinning processes disclosed in U.S.Pat. Nos. 3,802,817; 5,545,371; and 5,885,909; which are herebyincorporated by reference. According to the preferred high speed meltspinning process, one or more extruders supply melted polymer to a spinblock where the polymer is extruded through a plurality of openings toform a curtain of filaments. The filaments are partially cooled in anair quenching zone. The filaments are then pneumatically drawn to reducetheir size and impart increased strength. The filaments are deposited ona moving belt, scrim or other fibrous layer. Fibers produced by thepreferred high speed melt spinning process are substantially continuousand have a diameter of from 5 to 30 microns. These fibers can beproduced as single component fibers, as multiple component fibers, or assome combination thereof. Multiple component meltspun fibers can be madein various known cross-sectional configurations, including side-by-side,sheath-core, segmented pie, or islands-in-the-sea configurations.

[0043] An apparatus for producing nonwoven webs of high strengthbicomponent meltspun fibers at high speeds is schematically illustratedin FIG. 5. In this apparatus, two thermoplastic polymers are fed intothe hoppers 40 and 42, respectively. The polymer in hopper 40 is fedinto the extruder 44 and the polymer in the hopper 42 is fed into theextruder 46. The extruders 44 and 46 each melt and pressurize thepolymer and push it through filters 48 and 50 and metering pumps 52 and54, respectively. The polymer from hopper 40 is combined with polymerfrom hopper 42 in the spin block 56 by known methods to produce thedesired multiple component filament cross sections mentioned above, asfor example by using a multi-component spin block like that disclosed inU.S. Pat. No. 5,162,074, which is hereby incorporated by reference.Where the filaments have a sheath-core cross section, a lower meltingpolymer is typically used for the sheath layer so as to enhance thermalbonding. If desired, single component fibers can be spun from themultiple component apparatus shown in FIG. 5 by simply putting the samepolymer in both of the hoppers 40 and 42.

[0044] The melted polymers exit the spin block 56 through a plurality ofcapillary openings on the face of the spinneret 58. The capillaryopenings may be arranged on the spinneret face in a conventional pattern(rectangular, staggered, etc.) with the spacing of the openings set tooptimize productivity and fiber quenching. The density of the openingsis typically in the range of 500 to 8000 holes/meter width of the pack.Typical polymer throughputs per opening are in the range of 0.3 to 5.0g/min.

[0045] The filaments 60 extruded from the spin block 56 are initiallycooled with quenching air 62 and then drawn by a pneumatic draw jet 64before being laid down. The quenching air is provided by one or moreconventional quench boxes that direct air against the filaments at arate of about 0.3 to 2.5 m/sec and at a temperature in the range of 5°to 25° C. Typically, two quench boxes facing each other from oppositesides of the line of filaments are used in what is known as a co-currentair configuration. The distance between the capillary openings and thedraw jet may be anywhere from 30 to 130 cm, depending on the fiberproperties desired. The quenched filaments enter the pneumatic draw jet64 where the filaments are drawn by air 66 to fiber speeds in the rangeof from 2000 to 12,000 m/min. This pulling of the filaments draws andelongates the filaments near the spinneret face as the filaments passthrough the quench zone. The filaments 67 exiting the draw jet 64 arethinner and stronger than the filaments that were extruded from the spinblock. The substantially continuous filaments 67 are strong fibershaving a tensile strength of at least 1 gpd, and preferably having aneffective diameter of from 5 to 30 microns. The filaments 67 aredeposited onto a laydown belt or forming screen 68 as substantiallycontinuous filaments. The distance between the exit of the draw jet 64and the laydown belt is varied depending on the properties desired inthe nonwoven web, and generally ranges between 13 and 76 cm. A vacuumsuction is usually applied through the laydown belt to help pin thefiber web. Where desired, the resulting web 12 can be passed betweenthermal bonding rolls 72 and 74 before being collected on the roll 78.

[0046] The composite nonwoven fabric of the invention can be producedin-line using the apparatus that is shown schematically in FIG. 6.Alternatively, the layers of the composite sheet can be producedindependently and later combined and bonded to form the composite sheet.The apparatus shown in FIG. 6 includes spunbonded web productionsections 80 and 94 that are preferably like the high speed melt spinningapparatus described with regard to FIG. 5. The apparatus of FIG. 6further includes a meltblown web production section 82 incorporating themeltblowing apparatus of the type described with regard to FIG. 4. Forpurposes of illustration, the two spunbond web production sections 80and 94 are shown making bicomponent fibers. It is contemplated that thespunbond web production sections 80 and 94 could be replaced by unitsdesigned to produce spunbond webs having just one polymer component orhaving three or more polymer components. It is also contemplated thatmore than one spunbond web production section could be used in series toproduce a web made of a blend of different single or multiple componentfibers. It is further contemplated that the polymer(s) used in section94 could be different than the polymer(s) used in section 80. Where itis desired to produced a composite sheet having just one spunbond layerand one fine fiber layer (as shown in FIG. 3), the second spunbond webproduction section 94 can be turned off or eliminated.

[0047] According to the preferred embodiment of the invention, in thespunbond web production sections 80 and 94 of the apparatus shown inFIG. 6, two thermoplastic polymer components A and B are melted,filtered and metered (not shown) to the spin blocks 56 and 96 asdescribed above with regard to FIG. 4. The melted polymer filaments 60and 100 are extruded from the spin blocks through spinneret sets 58 and98, respectively, as described above with regard to FIG. 5. Thefilaments may be extruded as bicomponent filaments having a desiredcross section, such as a sheath-core filament cross section. Preferably,a lower melting temperature polymer is used for the sheath section whilea higher melting temperature polymer is used for the core section. Theresulting filaments 60 and 100 are cooled with quenching air 62 and 102as described above. The filaments next enter pneumatic draw jets 64 and104 and are drawn by drawing air 66 and 106 as described above withregard to FIG. 5. The fibers 67 from the spunbond web production section80 are deposited onto forming screen 68 so as to form a spunbond layer12 on the belt.

[0048] According to the preferred embodiment of the invention, twothermoplastic polymer components C and D are combined to make ameltblown bicomponent web in the meltblown web production section 82. Atleast one of these components comprises a blend of two or more differentpolymers. The polymer blend component is preferably formed by mixingpellets of the two polymers and extruding them together. The secondpolymer component may be a single polymer or another polymer blendformed in the same manner. The polymer components C and D are melted,filtered, and then metered (not shown) into the meltblowing spin block84. The melted polymers are combined in the spin block 84 and exit thespin block through a line of capillary openings in die like thosedescribed above with regard to FIG. 4. Preferably, the spin block 84generates the desired side-by-side fiber cross section. Alternative spinblock arrangements can be used to produce alternative fiber crosssections, such as a sheath-core cross section. A jet of gas 88, such ashot air, supplied from the channels 90 impacts on opposite sides of theexiting filaments 91 and attenuates each filament 91 immediately aftereach filament exits its capillary opening to form meltblown fibers. Themeltblown fibers 91 are deposited onto spunbond layer 12 to create thecohesive multiple component meltblown web layer 14.

[0049] Where a second spunbond web production section 94 is used,substantially continuous spunbond fibers 107 from the spunbond webproduction section 80 may be deposited onto the meltblown layer 14 so asto form a second spunbond layer 16 on web. The layers 12 and 16 do notnecessarily have to have the same composition, thickness or basisweight.

[0050] The spunbond-meltblown-spunbond web structure is passed betweenthermal bonding rolls 72 and 74 in order to produce the compositenonwoven web 10 which is collected on a roll 78. Preferably, the bondingrolls 72 and 74 are heated rolls maintained at a temperature within plusor minus 20° C. of the lowest melting temperature polymer in thecomposite. For a polyethylene-containing composite sheet, a bondingtemperature in the range of 115-120° C. and a bonding pressure in therange of 350-700 N/cm can be applied to obtain good thermal bonding.Alternative methods for bonding the layers of the composite sheetinclude calender bonding, ultrasonic bonding, through-air bonding, steambonding, and adhesive bonding.

Test Methods

[0051] In the description above and in the non-limiting examples thatfollow, the following test methods were employed to determine variousreported characteristics and properties. ASTM refers to the AmericanSociety for Testing and Materials, and AATCC refers to the AmericanAssociation of Textile Chemists and Colorists.

[0052] Basis Weight is a measure of the mass per unit area of a fabricor sheet and was determined by ASTM D-3776, which is hereby incorporatedby reference, and is reported in g/m².

[0053] Hydrostatic Head is a measure of the resistance of the sheet topenetration by liquid water under a static pressure. The test wasconducted according to AATCC-127, which is hereby incorporated byreference, and is reported in centimeters.

[0054] Frazier Air Permeability is a measure of air flow passing througha sheet under at a stated pressure differential between the surfaces ofthe sheet and was conducted according to ASTM D 737, which is herebyincorporated by reference, and is reported in m³/min/m².

[0055] This invention will now be illustrated by the followingnon-limiting examples which are intended to illustrate the invention andnot to limit the invention in any manner.

EXAMPLES Comparative Example A

[0056] This example demonstrates preparation of a SMS sheet bysandwiching and bonding a bicomponent meltblown layer between twobicomponent spunbond layers. The bicomponent meltblown layer is made ofbicomponent meltblown fibers containing two polymer components whereineach polymer component is a single polymer.

[0057] A meltblown bicomponent web was made with a polyethylenecomponent and a poly(ethylene terephthalate) component. The polyethylenecomponent was made from linear low density polyethylene with a meltindex of 150 g/10 minutes (measured according to ASTM D-1238) availablefrom Dow as ASPUN 6831A. The polyester component was made frompoly(ethylene terephthalate) with an intrinsic viscosity of 0.53 (asmeasured in U.S. Pat. No. 4,743,504) available from DuPont as Crystar®polyester (Merge 4449). The polymer was crystalized and dried prior toextrusion. The polyethylene polymer was heated to 450° F. (232° C.) andthe polyester polymer was heated to 572° F. (300° C.) in separateextruders. The two polymers were separately extruded, filtered andmetered to a bicomponent spin block arranged to provide a side-by-sidefiber cross section. The die of the spin block was heated to 599° F.(315° C.). The die had 601 capillary openings arranged in a 24 inch (61cm) line. The polymers were spun through the each capillary at a polymerthroughput rate of 0.80 g/hole/min. Attenuating air was heated to atemperature of 612° F. (322° C.) and supplied at a rate of 420 standardcubic feet per minute (scfm) (11.9 m³/min) through two 0.8 mm wide airchannels. The two air channels ran the length of the 24 inch line ofcapillary openings, with one channel on each side of the line ofcapillaries set back 1 mm from the capillary openings. The polyethylenewas supplied to the spin block at a rate of 23.1 kg/hr and the polyesterwas supplied to the spin block at a rate of 5.8 kg/hr. A bicomponentmeltblown web was produced that was 80 weight percent polyethylene and20 weight percent polyester. The meltblown fibers were collected on amoving forming screen to produce a meltblown web. Operating themeltblowing process under the conditions of this example resulted in theformation of a significant amount of “fly”, i.e. broken filaments thatwere blown away from the laydown zone by the attenuating air stream. Themeltblown web was collected on a roll. The meltblown web had a basisweight of 17.5 g/m².

[0058] The spunbond outer layers were made from bicomponent fibers witha sheath-core cross section. The spunbond fibers were made using anapparatus like that described above with regard to FIG. 5. Spunbond webswith a basis weight of 15 g/m² were produced for use in the outer layersof the composite sheet. The spunbond bicomponent fibers were made fromlinear low density polyethylene with a melt index of 27 g/10 minutes(measured according to ASTM D-1238) available from Dow as ASPUN 6811A,and poly(ethylene terephthalate) polyester with an intrinsic viscosityof 0.53 (as measured in U.S. Pat. No. 4,743,504) available from DuPontas Crystar® polyester (Merge 3949). The polyester resin was crystallizedat a temperature of 180° C. and dried at a temperature of 120° C. to amoisture content of less than 50 ppm before use.

[0059] The polyester was heated to 290° C. and the polyethylene washeated to 280° C. in separate extruders. The polymers were extruded,filtered and metered to a bicomponent spin block maintained at 295° C.and designed to provide a sheath-core filament cross section. Thepolymers were spun through the spinneret to produce bicomponentfilaments with a polyethylene sheath and a poly(ethylene terephthalate)core. The total polymer throughput per spin block capillary was 0.4g/min. The polymers were metered to provide fibers that were 30%polyethylene (sheath) and 70% polyester (core), based on fiber weight.The filaments were cooled in a 15 inch (38.1 cm) long quenching zonewith quenching air provided from two opposing quench boxes a temperatureof 12° C. and velocity of 1 m/sec. The filaments passed into a pneumaticdraw jet spaced 20 inches (50.8 cm) below the capillary openings of thespin block where the filaments were drawn at a rate of approximately9000 m/min. The resulting smaller, stronger substantially continuousfilaments were deposited onto a laydown belt with vacuum suction. Thefibers in the webs had an effective diameter in the range of 6 to 8microns. The resulting webs were passed between two thermal bondingrolls to lightly tack the web together for transport using a pointbonding pattern at a temperature of 100° C. and a nip pressure of 100N/cm. The line speed during bonding was 150 m/min. The lightly bondedspunbond webs were each collected on a roll.

[0060] The composite nonwoven sheet was prepared by unrolling the 15g/m² basis weight spunbond web onto a moving belt. The meltblownbicomponent web was unrolled and laid on top of the moving spunbond web.A second roll of the 15 g/m² basis weight spunbond web was unrolled andlaid on top of the spunbond-meltblown web to produce aspunbond-meltblown-spunbond composite nonwoven web. The composite webwas thermally bonded between an engraved oil-heated metal calender rolland a smooth oil heated metal calender roll. Both rolls had a diameterof 466 mm. The engraved roll had a chrome coated non-hardened steelsurface with a diamond pattern having a point size of 0.466 mm², a pointdepth of 0.86 mm, a point spacing of 1.2 mm, and a bond area of 14.6%.The smooth roll had a hardened steel surface. The composite web wasbonded at a temperature of 120° C., a nip pressure of 350 N/cm, and aline speed of 50 m/min. The bonded composite sheet was collected on aroll. The final basis weight of this composite nonwoven sheet was 51.6g/m².

Example 1

[0061] This example demonstrates preparation of a SMS sheet according tothe current invention. The SMS sheet was made by sandwiching and bondinga bicomponent meltblown layer between two bicomponent spunbond layers.The SMS sheet was substantially identical to the SMS sheet ofComparative Example A, except that the bicomponent meltblown layer wasmade from two polymer components wherein one polymer component is ablend of two polymers and the second polymer component is a singlepolymer.

[0062] A composite sheet was formed according to the procedure ofComparative Example A except the polyethylene component in the meltblownweb was made up of a blend of 90% by weight Dow ASPUN 6831A and 10% byweight Hoechst Celanese 1300A poly(butylene terephthalate). Thepoly(butylene terephthalate) acts as a spinning aid to the polyethylene.Also, the meltblowing process was altered as follows: thepolyethylene/poly(butylene terephthalate) blend was heated to 260° C.and the attenuating air flow rate was changed to 425 scfm (12.04m³/min). During operation of the meltblowing process, no formation of“fly” was observed. Process conditions for the meltblowing processes forComparative Example A and Example 1 are summarized in Table 1. Thephysical properties of the meltblown webs and composite SMS sheets arereported in Table 2.

[0063] Comparing Example 1 with Comparative Example A shows that thehydrostatic head is higher for the web of Example 1 with thepoly(butylene terephthalate) in the polyethylene component than the webof Comparative Example A, which was substantially identical to the webof Example 1, except for the absence of the poly(butylene terephthalate)in the polyethylene component of the web of Comparative Example A. It isbelieved that the improved hydrostatic head of Example 1 results from animprovement in the web uniformity when a blend of polymers is used asone of the polymer components in the multiple component meltblownfibers. TABLE 1 MELTBLOWN PROCESS CONDITIONS T_(PE) T_(PET) T_(Die) AirFlow Throughput Weight PE Weight PET Weight Ratio Example (° C.) (° C.)(° C.) (scfm)** (g/hole/min) (kg/hr) (kg/hr) (% PE) A 232 300 315 4200.80 23.1 5.8 80 1* 260 300 315 425 0.80 23.1 5.8 80

[0064] TABLE 2 NONWOVEN WEB PROPERTIES Basis Basis Hydro- Frazier Airweight of weight of static Permeability of Weight Meltblown CompositeHead of Composite Ratio Web Sheet Composite Sheet Example (% PE) (g/m²)(g/m²) Sheet (cm) (m³/min/m²) A 80 17.5 51.6 55.3 17.4 1* 80 15.9 49.972.0  9.8

Comparative Example B

[0065] This example demonstrates formation of a bicomponent meltblownweb in which the first component is a high viscosity polypropylene andthe second component is a low viscosity polypropylene.

[0066] A meltblown bicomponent web was made with a high viscositypolypropylene component (PP 1) and a low viscosity polypropylenecomponent (PP2). The high viscosity polypropylene component was madefrom a polyproylene resin with a melt flow rate of 35 (ASTM D1238-00)available from Exxon as 3155. The low visoscity polypropylene componentwas made from a polypropylene resin with a melt flow rate of 1200 (ASTMD1238-00) available from Exxon as 3546G. Both polymers were heated to550° F. (288° C.) in separate extruders. The two polymers wereseparately extruded, filtered, and metered to a bicomponent spin blockarranged to provide a side-by-side filament cross section. The die ofthe spin block was heated to 550° F. (288° C.). The die had 601capillary openings arranged in a 24 inch (61 cm) line. The polymers werespun through the each capillary at a polymer throughput rate of 0.40g/hole/min. Attenuating air was heated to a temperature of 550° F. (288°C.) and supplied at a rate of 300 standard cubic feet per minute (8.5m³/min) through two 2 mm wide air channels. The two air channels ran thelength of the 24 inch line of capillary openings, with one channel oneach side of the line of capillaries set back 2 mm from the capillaryopenings. Both polypropylene resins were supplied to the spin block at arate of 9.0 kg/hr. A bicomponent meltblown web was produced that was 50weight percent high viscosity polypropylene and 50 weight percent lowviscosity polypropylene. The meltblown fibers were collected on a movingforming screen to produce a meltblown web which was collected on a roll.The meltblown web had a basis weight of about 19 g/m².

Example 2

[0067] This example demonstrates formation of a bicomponent meltblownweb according to the current invention in which the first component is ablend of high viscosity polypropylene and linear low densitypolyethylene and the second component is a low viscosity polypropylene.

[0068] Multiple component meltblown webs were formed according to theprocedure of Comparative Example B except the high viscositypolypropylene component (PP1) was made up of a blend of Equistar GA594linear low density polyethylene and Exxon 3155 polypropylene. In Example2-1 the high viscosity polypropylene was blended with the Equistarlinear low density polyethylene to provide a blend made up of 25 weightpercent high viscosity polypropylene and 75 weight percent linear lowdensity polyethylene; in Example 2-2 the high viscosity polypropylenewas blended with 50 weight percent of linear low density polyethylene;and in Example 2-3 the high viscosity polypropylene was blended with thelinear low density polyethylene to provide a blend made up of 75 weightpercent high viscosity polypropylene and 25 weight percent linear lowdensity polyethylene. The physical properties of the meltblown webs arereported in Table 3 below.

[0069] A visual comparison of the meltblown webs of Example 2, whichwere identical to the meltblown web of Comparitive Example B except forthe absence of the polyethylene blend component in the web ofComparative Example B, showed that the visual uniformities of theExample 2 webs were much better than the uniformity of the web ofComparative Example B. This observation was confirmed with a lowermeasured Frazier air permeability value for the meltblown webs ofExample 2, as shown in Table 3 below. A lower Frazier air permeabilityis generally associated with better web formation and with finer fiberdiameters. TABLE 3 MELTBLOWN PROCESS CONDITIONS AND MELTBLOWN WEBPROPERTIES Basis Weight Weight Weight Weight Weight of Frazier Air Exam-% PE PP1 PP2 Ratio Meltblown Permeability ple in P1 (kg/hr) (kg/hr) (%PP1) (g/m²) (m³/min/m²) B 0 9.0 9.0 50 19 166 2-1* 75 4.5 13.5 25 20 402-2* 50 9.0 9.0 50 20 77 2-3* 25 13.5 4.5 75 20 123

What is claimed is:
 1. A multiple component meltblown web comprised ofat least 95% by weight of multiple component meltblown fibers having anaverage effective diameter of less than 10 microns, the multiplecomponent meltblown fibers comprised of a first polymer component and asecond polymer component distinct from the first polymer component, thefirst polymer component being comprised of from 1% to 99% by weight of afirst polymer and from 99% to 1% by weight of a second polymer whereinthe first and second polymers are selected from the group consisting ofpolyolefins, polyesters, polyamides, polystyrene, polyurethanes,fluoropolymers, olefinic ionomer resins, random co-polymers of ethyleneand methacrylic acid, and random co-polymers of ethylene and vinylacetate.
 2. The web according to claim 1, wherein the first polymercomponent is comprised of from 5% to 95% by weight of the first polymerand from 95% to 5% by weight of the second polymer.
 3. The web accordingto claim 2, wherein the first polymer component is comprised of from 10%to 90% by weight of the first polymer and from 90% to 10% by weight ofthe second polymer.
 4. The web according to claim 3 wherein the firstand second polymers are selected from the group consisting ofpolyethylene, polypropylene, poly(ethylene terephthalate),poly(trimethylene terephthalate), poly(butylene terephthalate),poly(hexamethylene adipamide), poly(ε-caprolactam), random co-polymersof ethylene and methacrylic acid, ionomeric random co-polymers ofethylene and methacrylic acid, polyurethanes comprising4,4-diphenyl-methane diisocyanate hard segments and polyether-basedpolyol soft segments, polyurethanes comprising 4,4-diphenyl-methanediisocyanate hard segments and polyester-based polyol soft segments, andrandom co-polymers of ethylene and vinyl acetate.
 5. The web accordingto claim 3 wherein the first polymer is a polyolefin and the secondpolymer is a polyester.
 6. The web according to claim 5 wherein thefirst polymer is selected from the group consisting of polyethylene andpolypropylene and the second polymer is selected from the groupconsisting of poly(ethylene terephthalate), poly(trimethyleneterephthalate), and poly(butylene terephthalate)
 7. The web according toclaim 6 wherein the second polymer component is selected from the groupconsisting of polyolefins and polyesters.
 8. The web according to claim7 wherein the second polymer component is a polyester.
 9. The webaccording to claim 8 wherein the first polymer is polyethylene, thesecond polymer is poly(butylene terephthalate), and the second polymercomponent is poly(ethylene terephthalate).
 10. The web according toclaim 3 wherein the first polymer is polypropylene and the secondpolymer is polyethylene.
 11. The web according to claim 10 wherein thesecond polymer component is polypropylene.
 12. The web according toclaim 3 wherein the first polymer is a polyolefin and the second polymeris an olefinic ionomer resin.
 13. The web according to claim 12 whereinthe second polymer component is a polyester.
 14. The web according toclaim 13 wherein the first polymer is polyethylene, the second polymeris an ionomeric random co-polymer of ethylene and methacrylic acid, andthe second polymer component is poly(ethylene terephthalate).
 15. Amultiple component meltblown web comprised of at least 95% by weight ofmeltblown fibers having an average effective diameter of less than 10microns, the meltblown fibers comprised of a first polymer component anda second polymer component distinct from the first polymer component,the first polymer component being comprised of from 1% to 99% by weightof a first polymer and from 99% to 1% by weight of a second polymerwherein the first and second polymers consist essentially ofnon-elastomeric polymers.
 16. The web according to claim 15 wherein thefirst and second polymeric components consist essentially ofnon-elastomeric polymers.
 17. A multiple component meltblown webcomprised of at least 95% by weight of meltblown fibers having anaverage effective diameter of less than 10 microns, the meltblown fiberscomprised of a first polymer component and a second polymer componentdistinct from the first polymer component, the first polymer componentbeing comprised of from 1% to 99% by weight of a first polymer and from99% to 1% by weight of a second polymer wherein the first and secondpolymers consist essentially of elastomeric polymers.
 18. The webaccording to claim 17 wherein the first and second polymeric componentsconsist essentially of elastomeric polymers.
 19. The web according toeither of claim 15 or 17 wherein the first polymer component comprisesfrom 5% to 95% by weight of the first polymer and from 95% to 5% byweight of the second polymer.
 20. The web according to claim 19 whereinthe first polymer component comprises from 10% to 90% by weight of thefirst polymer and from 90% to 10% by weight of the second polymer. 21.The web according to any of claim 3, 15, or 17 wherein the multiplecomponent fibers are bicomponent fibers.
 22. The web according to claim21 wherein the first and second polymer components are arranged in aside-by-side arrangement.
 23. The web according to claim 21 wherein thefirst and second polymer components are arranged in a sheath-corearrangement.
 24. A composite sheet comprising: a first fibrous layerhaving a first side and an opposite second side; a second fibrous layerbonded to the first side of the first fibrous layer; the first fibrouslayer being a multiple component meltblown web comprised of at least 95%by weight of multiple component meltblown fibers having an averageeffective diameter of less than 10 microns, the multiple componentmeltblown fibers comprised of a first polymer component and a secondpolymer component distinct from the first polymer component, the firstpolymer component being comprised of from 1% to 99% by weight of a firstpolymer and from 99% to 1% by weight of a second polymer; the secondfibrous layer comprised of at least 95% by weight of second layer fibershaving an average effective diameter that is greater than the averageeffective diameter of the meltblown fibers of the first fibrous layer.25. The sheet according to claim 24, wherein the first polymer componentbeing comprised of from 5% to 95% by weight of the first polymer andfrom 95% to 5% by weight of the second polymer.
 26. The sheet accordingto claim 25, wherein the first polymer component being comprised of from10% to 90% by weight of the first polymer and from 90% to 10% by weightof the second polymer.
 27. The sheet according to claim 26, wherein thefirst and second polymers and the second polymer component are selectedfrom the group consisting of polyolefins, polyesters, polyamides,polystyrene, polyurethanes, fluoropolymers, olefinic ionomer resins,random co-polymers of ethylene and methacrylic acid, and randomco-polymers of ethylene and vinyl acetate.
 28. The sheet according toclaim 27, wherein the first and second polymers and the second polymercomponent are selected from the group consisting of polyolefins andpolyesters.
 29. The sheet according to claim 28 wherein the polyolefinis selected from the group consisting of polyethylene and polypropyleneand the polyester is selected from the group consisting of poly(ethyleneterephthalate), poly(trimethylene terephthalate), and poly(butyleneterephthalate).
 30. The sheet according to claim 29, wherein the firstpolymer is polyethylene, the second polymer is poly(butyleneterephthalate), and the second polymer component is poly(ethyleneterephthalate).
 31. The sheet according to claim 27 wherein the multiplecomponent meltblown fibers are bicomponent fibers and the second fibrouslayer is a spunbond layer.
 32. The sheet according to claim 31 whereinthe spunbond layer comprises bicomponent spunbond fibers.
 33. The sheetaccording to claim 32 wherein the polymer components of the meltblownfibers are arranged in a side-by-side configuration and the spunbondfibers are sheath-core fibers.